Temperature adjusting and compressing in injection stretch blow molding for forming raised portions in the container produced

ABSTRACT

A process for forming a hollow container from a hot closed-end parison includes the steps of injection molding a hot closed-end parison, adjusting the temperature of the hot closed-end parison by heating or cooling the hot closed-end parison in a predetermined location within a temperature adjusting pot in a temperature adjusting device. The parison is then blow-molded into a hollow container having a predetermined configuration after the parison has been adjusted in temperature. The temperature adjusting step uses at least either of the temperature adjusting pot or a temperature adjusting core in the temperature adjusting device so as to apply a pre-treatment, such as by clamping, to a portion of said hot closed-end parison for obtaining a predetermined concavo-convex pattern in the hollow container formed at the subsequent blowing step. Thus, a hollow container, a portion of which has the desired concavo-convex pattern, can be mass-produced simply and inexpensively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process of blowing hollow containerssuch as bottles or the like from closed-end parisons and particularly toan injection/stretch/blow molding process for forming a predeterminedconcavo-convex pattern in the bottom of a hollow container.

2. Description of the Related Art

There are well-known injection/stretch/blow molding techniques which areutilized to blow hollow containers such as bottles from synthetic resinmaterials such as polyethylene terephthalate (PET). The hollowcontainers thus blown are transparent with surface gloss as in glassbottles and superior in various properties such as resistance to shock,air blocking, handling for design, mass-productivity and so on. For suchreasons, the hollow blown containers are currently used for variousfluid materials such as cold drinks, powdered detergents and the like.

However, such hollow blown containers are easily deformable since thewall thickness thereof is small. For example, if they are used aspressurized liquid containers for carbonated beverages and beers, thewalls and particularly the base portions in the containers are easilydeformable due to the internal pressure from the contents thereof. Thebase portions of the hollow blown containers are required to bestrengthened sufficiently to resist the internal pressure described aswell as drop test.

In order to overcome such problems, it has been proposed that thebottoms of the hollow blown containers were formed with concavo-convexpatterns and particularly strengthening ribs, as in Japanese Laid-OpenPatent Application 79238/1980.

This proposal uses a core utilized to injection mold a parison andhaving a concavo-convex pattern formed therein. The core is used so asto provide a closed-end parison having its bottom in which strengtheningribs are formed by the concavo-convex pattern during molding.

However, this proposal can be applied only to the so-called cold parisontechnique, but not to the hot parison technique in which immediatelyafter a parison has been injection molded, it is blown utilizing itspotential heat.

In other words, the injection/stretch/blow molding technique for blowmolding hollow containers from closed-end parisons frequently utilizesthe hot parison technique for blow molding hollow containers by the useof potential head in parisons immediately after they have been injectionmolded.

In the hot parison technique, the distribution of temperature in the hotclosed-end parison highly influences the wall thickness of a hollowcontainer to be blown.

It is thus required to injection mold a hot closed-end parison withoutcreation of irregularity in temperature.

The injection molding of the closed-end parison is accomplished byinjecting a synthetic resin material such as PET into a small moldcavity which is surrounded by a core and mold halves. If the core soused is formed, at its tip, with a rib-shaped concavo-convex pattern inthe prior art, the flow of injected material will be disturbed toprovide uneven wall thickness in the resulting parison, leading to anirregularity in temperature. Accordingly, such a technique could not beapplied to the hot parison technique.

When it is particularly desired to produce a PET bottle having its verycomplicated configuration, a closed-end parison itself used thereforfrequently has a complicated configuration. If such a closed-end parisonis to be injection molded, it is required to control the injectionmolding procedure such that the flow of PET in the mold cavity will notbe disturbed as much as possible, without creation of irregularity intemperature. It is not absolutely acceptable to provide a rib-shapedconcavo-convex pattern on the tip of the core used to form the moldcavity.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aninjection/stretch/blow molding process wherein a hollow container can besimply and easily formed with the bottom thereof strengthened by aconcavo-convex pattern and preferably a rib-shaped pattern.

To this end, the present invention provides a process comprising thesteps of:

injection molding a closed-end parison;

adjusting the temperature in said closed-end parison by heating orcooling the necessary part of said closed-end parison within atemperature adjusting pot in temperature adjusting means; and

blowing said closed-end parison adjusted with respect to its temperatureinto a hollow container having a desired configuration;

said temperature adjusting step using at least either of said pot or atemperature adjusting core in the temperature adjusting means so as toapply a pre-treatment to the bottom portion of said hot closed-endparison for obtaining a predetermined concavo-convex pattern in thebottom portion of a hollow container formed in the subsequent blowingstep.

The term "closed-end parison" used herein is intended to include somepreform which can be molded in accordance with the principle of thepresent invention, other than the closed-end parison.

As is well-known, the closed-end parison has a relatively high internaltemperature immediately after injection molding. It is also well-knownthat the average resin temperature across the wall of a parisonimmediately after injection molding is higher at the thicker wallportion than at the thinner wall portion of the parison.

If such a closed-end parison is blown as it is, therefore, the wallportion thereof being higher in internal temperature will be morestretched while the other wall portion of the parison being lower ininternal temperature will be less drawn.

Such a process of blowing a closed-end parison having an internaltemperature is called "hot parison technique". The hot parison techniquefrequently performs an adjustment of temperature in which various partsof a hot closed-end parison are locally heated or cooled by atemperature adjusting pot in a temperature adjusting device so as toprovide a desired thickness throughout a hollow molded container.

In such an adjustment of temperature, the closed-end parison is normallyreceived within a temperature adjusting Pot. A temperature adjustingcore is then inserted into the parison through the open end thereof.

The process of the present invention is characterized by the temperatureadjusting step performed prior to the blowing step, wherein the bottomof a hot closed-end parison is previously treated to provide a hollowblown container having its bottom portion formed with a desiredconcavo-convex pattern, preferably a rib-shaped strengthening pattern.

In order to perform such a pre-treatment, for example, at least one ofthe temperature adjusting pot and core is previously formed with aconcavo-convex pattern which is to be formed in the bottom of a hotparison prior to the blowing step. The temperature adjusting core or potis located surrounding the bottom portion of the hot closed-end parisonand then compressed against that bottom portion. Since a series of stepsare performed against the hot closed-end parison while the internaltemperature thereof remains at its relatively high level, thecompression of the temperature adjusting core or pot against the bottomportion of the parison can simply and easily transfer the desiredconcavo-convex pattern from the core or pot to the bottom portion of thehot closed-end parison.

The hot closed-end parison thus pre-treated is then fed to thesubsequent blowing step wherein it will be formed into a hollowcontainer having its bottom portion formed with a concavo-convexstrengthening pattern and particular a rib-shaped strengthening pattern.

Alternatively, any one of the temperature adjusting pot or core may havea "temperature control pattern" portion which can provide finelydifferent temperature levels to the bottom of a hot closed-end parison,compatible with the concavo-convex strengthening pattern. Such a pot orcore can be similarly applied to compress it against the hot closed-endparison under a predetermined Pressure. Thus, the bottom portion of thehot closed-end parison will be pre-treated with differential temperaturecorresponding to the temperature control pattern. The pre-treatedparison is then fed to the blowing step wherein it is formed into ahollow container having its bottom patterned with the desiredstrengthening ribs.

In such a manner, the present invention provides a process which cansimply and easily form a hollow container having its bottom portionstrengthened by a concavo-convex or rib-shaped pattern without reductionof the productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 10 illustrate a first embodiment of the presentinvention.

FIG. 1 is a fragmentary view showing, in an enlarged scale, atemperature adjusting device which is one of the primary parts of thepresent invention.

FIG. 2 illustrates an injection/stretch/blow molding system taking thehot parison technique.

FIG. 3 is a schematic cross-section of a parison formed by the injectionmolding device in the first embodiment.

FIG. 4 is a schematic cross-section of the temperature adjusting deviceused in the first embodiment.

FIG. 5 is a plan view showing a concavo-convex pattern on the tip of thetemperature adjusting core shown in FIGS. 1 and 4.

FIG. 6 is a cross-sectional view of the bottom portion of a parison,onto which the concavo-convex pattern shown in FIG. 5 is transferredfrom the temperature adjusting core.

FIG. 7 schematically illustrates the blow molding device used in thesystem of the first embodiment.

FIGS. 8 through 10 schematically illustrate the bottom of a hollowcontainer formed by the use of the first embodiment system, FIG. 8 beinga plan view of the bottom;

FIG. 9 being a cross-sectional view taken along a line A--A' in FIG. 8;and

FIG. 10 being a cross-sectional view taken along a line B--B' in FIG. 8.

FIGS. 11 through 13 illustrate a second preferred embodiment of thepresent invention.

FIG. 11 illustrates a part of the temperature adjusting device which isan essential part in the present invention.

FIG. 12 is a plan view of a temperature control pattern portion on thetip of the temperature adjusting pot shown in FIG. 11.

FIG. 13 illustrates the distribution of temperature in the bottom of aparison, which is provided by the use of the temperature control patternshown in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described by way of example inconjunction with the drawings.

First Embodiment

Referring first to FIG. 2, there is shown a preferred form of aninjection/draw/blow molding apparatus relating to the present invention.The apparatus generally comprises an injection molding device 100 forinjection molding a hot closed-end parison; a temperature adjustingdevice 200 for adjusting the temperature of the hot closed-end parison;a blowing device 300 for blow molding a hollow container from the hotclosed-end parison after it has been adjusted in temperature; and aseparating device 400 for cutting the hollow container off the blowmolding device after the hollow container has been blown therein.

The injection molding device 100 injection molds a closed-end parison 10as shown in FIG. 3. The closed-end parison 10 includes a threaded neckportion 10a, a body portion 10b extending longitudinally from the neckportion 10a and a bottom portion 10c which will form the bottom of ahollow container after blown. An internal step 10d is formed in theconnection between the body portion 10b and the bottom portion 10c.

The bottom 10c is shown to be of a cup-shaped configuration including abottom face region and a side region, but may be formed to have a flatconfiguration. Since the internal step 10d is formed between thecup-shaped bottom portion 10c and the body portion 10b, the internaldiameter of the bottom portion 10c will be slightly smaller than that ofthe body portion 10b.

After being injection molded, the closed-end parison 10 is directlysupplied to the temperature adjusting device 200.

FIG. 4 shows the temperature adjusting device 200. Normally, the hotclosed-end parison 10 is held, at its neck portion 10a, by a neck moldsection 30 on a rotary disc 20. As the rotary disc 20 is rotated, theparison 10 is fed to the subsequent step while being held by the neckmold section 30.

The temperature adjusting device 200 comprises a temperature adjustingpot 210 for heating or cooling the closed-end parison 10 at the outerperiphery thereof and a temperature adjusting core 220 for heating orcooling the parison 10 from the interior thereof.

The temperature adjusting pot 210 includes an elevator means 216. Thetemperature adjusting core also includes an elevator means (not shown).Thus, the pot and core may be normally placed at their lower and upperretracted positions, respectively. When the parison 10 is moved to apredetermined position by the rotary disc 20, the temperature adjustingpot 210 is raised, by its elevator means 216, to a position wherein acenter ring 218 in the opened tip of the pot 210 engages the end of theneck mold section 210.

The temperature adjusting pot 210 also includes a plurality oftemperature adjusting blocks 212a, 212b for covering the barrel portionof the parison 10 and a temperature adjusting block 212c for surroundingthe outer periphery of the bottom portion 10c of the parison 10. Aninsulator 214 is provided to connect the adjacent blocks with eachother. It is usually required that the body portion 10b of the parison10 is sufficiently drawn on blowing. In the temperature adjusting step,therefore, the body portion of the parison must be heated up to adesired temperature. On the contrary, the bottom portion 10c of theparison has a variable temperature depending on the wall thickness ofthat bottom portion to be formed. If the bottom portion of the parisonis to have a thicker wall, it must be cooled up to some extent oftemperature. If it is desired to provide a smaller wall thickness in thebottom portion, the parison should be heated up to a predetermined levelof temperature at its bottom. In the first embodiment, it is assumedthat the bottom portion 10c of the parison 10 is cooled down to apredetermined temperature in order to provide a thicker wall in thebottom portion 10c.

For such a purpose, the plurality of temperature adjusting blocks 212aand 212b are utilized as heating blocks surrounding the barrel portion10b of the parison 10 while the temperature adjusting block 212ccovering the bottom portion 10c is used as cooling block. Thetemperature adjusting pot 210 is organized such that when the centerring 218 on the opened end of the pot is engaged by the neck moldsection 30, the cooling block 212c is sealingly pressed against thebottom portion 10c of the parison 10 under a predetermined pressure.

The temperature adjusting core 220 is lowered into the interior of theparison 10 from above the rotary disc 20 past the interior of the neckmold section 30. The core 220 is stopped at a position in which the tipthereof is sealingly pressed against the inner wall of the bottomportion 10c.

The temperature adjusting core 220 includes a heating and coolingmechanism (not shown) which is adapted to heat or cool the barrel andbottom portions 10b, 10c of the parison 10. In the illustratedembodiment, the bottom portion 10c is being cooled.

Conventionally, the hot closed-end parison 10 is fed to and molded atthe blowing step into a hollow container after the parison has beenadjusted in temperature by the use of the temperature adjusting pot andcore 210, 220. Additionally, the present invention is characterized bythat it utilizes the temperature adjusting pot and core 210, 220 whichcan also press the bottom portion 10c of the parison 10 from theopposite sides thereof under a predetermined pressure. In such a manner,a pre-treating step can be made to the bottom portion 10c of the parisonto provide a desired concavo-convex pattern at the bottom portion of thehollow container during the blow molding step.

In order to perform such a pre-treatment, at least one of the tipportion of the temperature adjusting core 220 and the surface of thecooling block 212c may be formed with a concavo-convex pattern used formaking the pre-treatment on the bottom portion of the parison. When thebottom portion 10c of the parison 10 is clamped between the temperatureadjusting core 220 and the cooling block 212c under a predeterminedpressure, the aforementioned concavo-convex pattern will be transferredtherefrom to the bottom portion 10c of the parison 10. As a result, thebottom portion 10c will have different wall thickness at various parts.

Particularly, if the hot parison 10 maintains sufficient heat at theinterior of the wall thereof, the concavo-convex pattern can be simplyand easily transferred from the temperature adjusting core 220 and/orthe cooling block 212c to the bottom portion 10c when the latter isclamped between the core 220 and the cooling block 212c under apredetermined pressure. The parison 10 thus patterned is then fed to thesubsequent blowing step wherein a hollow container having its bottomportion with the concavo-convex pattern can be simply and easily formed.

FIG. 1 shows a preferred embodiment of the present invention in whichthe tip of the temperature adjusting core 220 includes a concavo-convexpattern 230 formed therein, the concavo-convex pattern being in turntransferred therefrom to the inner wall of the bottom portion 10c.

In this embodiment, the tip of the temperature adjusting core 220 has anexternal diameter slightly larger than the internal diameter of thebottom portion 10c of the parison 10. The concavo-convex pattern 230 onthe tip of the core 220 consists of a plurality of concentric ring-likegroove portions 230a spaced away from each other a predetermineddistance and a plurality of radial groove portions 230b extendingradially from the tip to the outer periphery, these radial grooves alsofunctioning as air vents, as shown in FIG. 5.

The procedure of clamping the bottom portion 10c of the parison 10between the temperature adjusting core 220 and the cooling block 212cmay be optionally set, if necessary. In this embodiment, the temperatureadjusting core 220 is inserted into the interior of the parison untilthe tip of the core 220 is brought into contact with the inner wall ofthe bottom portion 10c of the parison. In such a state, the elevatormeans 216 is initiated to move the cooling block 212c upwardly by adistance equal to about 0.5 mm to compress the bottom portion 10c sothat the concavo-convex pattern 230 will be transferred from the coolingblock to the inner wall of the bottom portion 10c.

Since the external diameter of the tip of the temperature adjusting core220 on which the concavo-convex pattern 230 is formed is slightly largerthan the internal diameter of the bottom portion 10c of the parison 10in this embodiment, the tip of the temperature adjusting core 220 willbe press fitted into the interior of the bottom portion 10c. Thus, theconcavo-convex pattern 230 can be well transferred from the tip of thetemperature adjusting core 220 to both the bottom and side face regionsof the bottom portion 10c through the entire internal surfaces thereof.

FIG. 6 is a cross-sectional view of the bottom portion 10c in FIG. 1,taken along a line VI--VI therein. As seen from FIG. 6, a plurality ofribs 10e are formed on the inner wall of the bottom portion 10c by thering-shaped and radial groove portions 230a and 230b in theconcavo-convex pattern 230.

As the transfer and temperature adjustment for the parison 10 iscompleted, the temperature adjusting core and pot 220, 210 are thenretracted upward and downward, respectively. Thereafter, the rotary disc20 is rotated to convey the parison 10 to the blowing device 300.

The blowing device 300 is shown in FIG. 7, which comprises a split mold310 having cavity faces adapted to define the configuration of afinished product and a stretching rod 320 for axially stretching theparison 10. By using the well-known technique, the blowing device 300can orient or strech and blow mold the parison 10 into a hollowcontainer.

Since the bottom portion 10c of the parison 10 is blown in accordancewith the transferred concavo-convex pattern, the bottom portion of ahollow container so formed will have a concavo-convex patterncorresponding to the aforementioned concavo-convex pattern 230.

FIGS. 8 to 10 show part of the hollow container 40 blown in such amanner. FIG. 8 shows the inner wall of the bottom portion 40a of thehollow container 40; FIG. 9 is a schematic cross-section of the bottomportion 40a taken along a line A--A'; and FIG. 10 is a schematiccross-section of the bottom portion 40a taken along a line B--B'.

As can seen from FIGS. 8 to 10, the bottom portion 40a of the hollowcontainer 40, which has been blow molded, is formed with a plurality ofconcentric ring-like strengthening ribs 42a and a plurality of radialstrengthening ribs 42b, which ribs 42a and 42b correspond to therespective groove portions 230a and 230b in the concavo-convex pattern230.

In such a manner, the present invention can simply and easily form thestrengthening ribs 42a and 42b in the desired pattern on the bottomportion 40a of the hollow container 40 only by making a predeterminedpre-treating step onto the bottom portion 10c of the parison 10 duringthe temperature adjusting step.

In this embodiment, particularly, the hollow container 40 can be moldedwith sufficient strength in its bottom portion 40a and withoutdisturbing the appearance of the hollow container, since these ribs 42aand 42b can be formed on the inner wall of the bottom portion 40a of thehollow container 40.

Second Embodiment

FIG. 11 to 13 show a second preferred embodiment of a temperatureadjusting device 200 in the injection stretch blow molding apparatus ofthe present invention. Parts similar to those of the first embodimentare denoted by similar reference numerals.

Although the first embodiment has been described as to theconcavo-convex pattern 230 on the tip of the temperature adjusting core220, which pattern is to be transferred therefrom to the bottom portionof the hollow product, the second embodiment utilizes a temperaturecontrol pattern 240 formed on the tip of the temperature adjusting core220 so as to provide a distribution of differential temperature having apattern corresponding to the aforementioned concavo-convex pattern to betransferred from the tip of the core 220 to the parison.

This temperature control pattern 240 consists of a plurality ofconcentrically spaced convex ring portions 240a about the central axisof the core tip and a plurality of radially extending convex portions240b from the central axis of the core tip to the peripheral edge of thesame.

The temperature adjusting core 220 is used as cooling core. Onoperation, the temperature control pattern 240 on the core tip ispressed against the inner wall of the bottom portion 10c of the parison10 to cool it through the convex portions 240a and 240b therein.

FIG. 13 shows a cross-section of the parison 10, taken along a lineVIII--VIII in FIG. 11. In this figure, reference numeral 10f denotesparts of the parison 10 which are cooled by the respective convexportions 240a and 240b in the temperature control pattern 240.

After the inner bottom wall of the parison 10 has been cooled only atportions corresponding to the temperature adjusting pattern 240, theparison 10 is fed to and molded at the blow molding step into a hollowcontainer 40 having its bottom portion 40a which is formed with ribs 42aand 42b corresponding to the convex portions 240a and 240b in thetemperature control pattern 240, respectively, as shown in FIGS. 8through 10.

This is because when the hollow container is formed in the blowing step,the wall thickness thereof can be highly influenced by differentialtemperature provided to the parison 10 in the temperature adjusting stepsince the hot parison is blow molded utilizing the potential heat in theinjection molded parison. More particularly, the parts 10f cooledthrough the convex portions 240a and 240b in the temperature controlpattern 240 are less stretched during the blow molding step. Thus, thering-like and radial strengthening ribs 42a and 42b will be formed inthe bottom portion 40a of the hollow container 40 during the blowmolding step.

Although the second embodiment has been described as to the temperaturecontrol pattern 240 having the convex portions 240a and 240b made of thesame material as that of the temperature adjusting core, the presentinvention is not limited to such a structure and may be applied to atemperature control pattern made of any other material different fromthat of the core in thermal conductivity.

Although the second embodiment has been described at to the temperaturecontrol pattern 240 constituted of the convex portions 240a and 240b, aplanar temperature control pattern may be obtained when the convex andconcave portions in the pattern are respectively made of materialsdifferent from each other in thermal conductivity.

The present invention is not limited to the embodiments illustrated anddescribed herein and may be applied in various modified and changedforms without departing the scope and spirit of the invention.

For example, the concavo-convex pattern 230 may be combined with thetemperature control pattern 240 in the tip of the temperature adjustingcore 220. In such a case, the groove portions 230a and 230b in theconcavo-convex pattern 230 may be formed of any suitable material havingits thermal conductivity higher than that of the convex portions in thesame pattern. Such a construction can more effectively cool the convexrib-like portions 10e transferred to the bottom portion 10c of theparison 10 as shown in FIG. 6. On the sequential blow molding step,these cooled convex portions 10e are less stretched. As a result, theconcavo-convex pattern consisting of the ribs 42a and 42b can be moreeffectively formed in the bottom portion 40a of the hollow container 40when being blow molded.

Although the embodiments have been described as to the concavo-convexpattern formed in the inner wall of the bottom portion 40a of the hollowcontainer 40, the present invention is not limited to such anarrangement and may be similarly applied to provide concavo-convexpatterns formed in the bottom portion 40a only at the outer wall or atboth the inner and outer walls. If a concavo-convex pattern is to beformed in the outer wall of the bottom portion 40a, the concavo-convexpattern 230 or the temperature control pattern 240 may be formed on thesurface of the cooling block 212c of the temperature adjusting pot 210in a manner similar to that of the described embodiments.

Although the embodiments have been described as to the rib-shapedpattern formed on the bottom portion 40a of the hollow container 40, anyother pattern may be similarly used in accordance with the presentinvention, if desired.

As will be apparent from the foregoing, the present invention canmass-produce hollow containers having their bottom portions formed withthe desired concavo-convex pattern simply and inexpensively by using atleast one of the temperature adjusting pot and core and performing apre-treatment for providing a desired concavo-convex pattern to thebottom portion of a hollow container to be blown, during the temperatureadjusting step wherein a hot closed-end parison is adjusted in internaltemperature.

I claim:
 1. A process comprising the steps of:injection molding a hotclosed-end parison; adjusting the temperature of said hot closed-endparison by heating or cooling said hot closed-end parison in at leastone predetermined location within a temperature adjusting pot in atemperature adjusting device; and blow molding the closed-end parisoninto a hollow container having a predetermined configuration after saidparison has been adjusted in temperature; said temperature adjustingstep using at least either of the temperature adjusting pot or atemperature adjusting core in said temperature adjusting device so as toapply pressure to said at least one predetermined location of said hotclosed-end parison by clamping and compressing said parison between saidtemperature adjusting pot and core to create a differential wallthickness in said at least one predetermined location for obtaining apredetermined concavo-convex pattern provided to a corresponding portionof said hollow container formed at said blow molding step.
 2. A processas defined in claim 1 wherein said temperature adjusting step performs:acompression for obtaining a concavo-convex rib-like pattern on thebottom portion of the hollow container formed int he subsequent blowingstep.
 3. A process as defined in claim 1 further comprising:before saidinjection molding step, forming a concavo-convex pattern on at least oneof said temperature adjusting pot and core int eh temperature adjustingdevice; and wherein said temperature adjusting step further comprisestransferring said concavo-convex pattern to the bottom portion of saidhot closed-end parison by clamping and compressing said parison betweensaid temperature adjusting core and pot under a predetermined pressure.4. A process as defined in claim 3 wherein said concavo-convexpattern:is formed on the temperature adjusting core and transferred fromsaid temperature adjusting core to the inner wall of the bottom portionof said hot closed-end parison.
 5. A process as defined in claim 4wherein said injection molding step further includes the step of:formingthe bottom portion of said hot closed-end parison into a cup-shapedconfiguration, said hot closed-end parison having a body portion, theinternal diameter of which is larger than that of the cup-shaped bottomportion and wherein said temperature adjusting step further includes thestep of: forming the tip of said temperature adjusting core with saidconcavo-convex pattern formed therein to have an external diameterslightly larger than the internal diameter of said hot closed-endparison at its bottom portion, the tip of said temperature adjustingcore being press fitted into the interior of the cup-shaped bottomportion of said hot closed-end parison, such that said concavo-convexpattern is transferred from said temperature adjusting core to the innerwall of the cup-shaped bottom portion of said hot closed-end parison. 6.A process as defined in claim 3 wherein said concavo-convex patterncomprises:a plurality of concentric ring-shaped groove portions spacedaway from each other a predetermined distance; and a plurality of radialgroove portions extending radially from the central axis of saidpattern, said radial groove portions also functioning as air vents.
 7. Aprocess as defined in claim 5 wherein said concavo-convex patterncomprises:a plurality of concentric ring-shaped groove portions spacedaway from each other a predetermined distance and a plurality of radialgroove portions extending radially from the central axis of saidpattern, said radial groove portions also functioning as air vents.
 8. Aprocess as defined in claim 3 wherein said temperature adjusting stepfurther includes the steps of:clamping the bottom portion of said hotclosed-end parison between the temperature adjusting core and pot; andthereafter moving at least one of said temperature adjusting core andpot toward the other by a predetermined amount to transfer theconcavo-convex pattern to the bottom of said hot closed-end parison. 9.A process as defined in claim 7 wherein said temperature adjusting stepfurther includes the steps of:clamping the bottom portion of said hotclosed-end , parison between the temperature adjusting core and pot; andthereafter moving at least one of said temperature adjusting core andpot toward the other by a predetermined amount to transfer theconcavo-convex pattern to the bottom of said hot closed-end parison. 10.A process comprising the steps of:forming a concavo-convex pattern on atleast one of a temperature adjusting pot and core in a temperatureadjusting device; injection molding a hot closed-end parison; adjustingthe temperature of said hot closed-end parison by heating or coolingsaid hot closed-end parison in at least one predetermined locationwithin the temperature adjusting pot in the temperature adjustingdevice; said temperature adjusting step further comprising: clamping thebottom portion of said hot closed-end parison between the temperatureadjusting core and pot and thereafter moving at least one of saidtemperature adjusting core and pot toward the other by a predeterminedamount, said concavo-convex pattern being transferred therefrom to thebottom portion of said hot closed-end parison by clamping andcompressing said parison between said temperature adjusting core and potunder a predetermined pressure thereby creating a differential wallthickness in the bottom portion of said hot closed end parison; and blowmolding the closed-end parison into a hollow container having apredetermined configuration after said parison has been adjusted intemperature thereby obtaining a predetermined concavo-convex pattern ona portion of said hollow container which corresponds to saidconcavo-convex pattern transferred to said hot closed-end parison.
 11. Aprocess comprising the steps of:injection molding a hot closed-endparison thereby forming a bottom portion of said hot closed-end parisoninto a cup-shaped configuration having an inner wall, said hotclosed-end parison having a body portion, the internal diameter of whichis larger than that of the cup-shaped bottom portion; adjusting thetemperature of said hot closed-end parison by heating or cooling saidhot closed-end parison in at least one predetermined location within atemperature adjusting pot in a temperature adjusting device; and blowmolding the closed-end parison into a hollow container having apredetermined configuration after said parison has been adjusted intemperature; said temperature adjusting step using a temperatureadjusting core having a tip with a concavo-convex pattern formed thereonin said temperature adjusting device to transfer the concavo-convexpattern from said temperature adjusting core to the inner wall of thebottom portion of said hot closed-end parison for obtaining apredetermined concavo-convex pattern provided to the bottom portion of ahollow container formed at the subsequent blowing step, wherein the tipof said temperature adjusting core is formed with said concavo-convexpattern formed therein having raised portions with an external diameterslightly larger than the internal diameter of said hot closed-endparison at its bottom portion, the tip of said temperature adjustingcore being press fitted into the interior of the cup-shaped bottomportion of said hot closed-end parison, such that said parison isclamped and compressed between said temperature adjusting pot an coreunder a predetermined pressure, for said transfer of said concavo-convexpattern to the inner wall of said hot closed-end parison to create adifferential wall thickness in said parison.